1. Field of the Invention
The present invention relates to a transformer and, more particularly, to an improved arrangement of a flyback transformer for use in a television receiver wherein the flyback transformer is installed with electric parts, such as variable resistors.
2. Description of the Prior Art
A flyback transformer for use in a television receiver generally includes a primary coil for receiving a low voltage and a secondary coil for producing a high voltage. The high voltage produced from the secondary coil is applied to a cathode ray tube for effecting the horizontal deflection.
According to a recent flyback transformer, a tap is provided intermediately on the secondary coil for producing a predetermined voltage used for focusing an image on the cathode ray tube and/or for applying a potential to a screen grid of the cathode ray tube. Since the voltage for focusing the image (hereinafter referred to as a focusing voltage) and the voltage for applying a potential to the screen grid (hereinafter referred to as a screen voltage) are required to be adjusted to predetermined voltages, a lead line extending from the tap is connected to first and second variable resistors, in which the first variable resistor is provided to produce the focusing voltage and the second variable resistor is provided to produce the screen voltage.
Initially, such variable resistors have been provided separately from the flyback transformer. However, from the view point of reducing the number of constructing parts, many approaches have been made to install the variable resistors on the flyback transformer. An example of one prior art flyback transformer installed with variable resistors is explained below.
Referring to FIGS. 1 and 2, the prior art flyback transformer installed with variable resistor(s) includes a casing 2, the primary and secondary coil mounted on inner and outer bobbins, respectively, (only the secondary coil is shown in FIG. 2 with reference numeral 4), and a lead line 6 extending from an intermediate tap 4a of the secondary coil 4. The end of the secondary coil 4 is connected to a cathode ray tube (not shown) through a lead line 10 for effecting the horizontal deflection. A ferrite core 8 having an O-shape configuration extends through the inner bobbin.
The prior art flyback transformer further includes a variable resistor unit 12 rigidly secured on the casing 2 by means of, e.g., securing screw. The variable resistor unit 12 as shown in FIG. 3 includes two pins 12a and 12b and a knob 12c. The pin 12a is provided for the connection with the lead line 6 which is extending outwardly from an opening formed at the bottom of the casing 2 and along a side wall of the casing to the variable resistor unit 12. When the knob 12c is turned, a variable resistor (not shown) incorporated in the unit 12 is so adjusted as to produce the focusing voltage. A similar variable resistor unit is further provided on the casing 2 for producing the screen voltage.
According to the above described prior art transformer, there are such disadvantages that the lead line 6 carrying a relatively high voltage extends outside the casing and, therefore, the maintenance of the flyback transformer is rather difficult and, at the same time, the size of the flyback transformer becomes bulky.
Another prior art flyback transformer (not shown) has a variable resistor unit incorporated inside the casing. According to this type of flyback transformer, the variable resistor unit is placed inside the casing before the casing is packed with synthetic resin. Therefore, the synthetic resin is casted in the casing to fixedly support the coils, variable resistor unit, and other components in the casing. Thus, the flyback transformer of this type has such a disadvantage that it is impossible to exchange the variable resistor.